RFR: 8342818: Implement JEP 509: JFR CPU-Time Profiling [v45]

[Markus Grönlund]

On Wed, 4 Jun 2025 11:18:52 GMT, Johannes Bechberger <jbechberger at openjdk.org> wrote:

>> This is the code for the [JEP 509: CPU Time based profiling for JFR](https://openjdk.org/jeps/509).
>> 
>> Currently tested using [this test suite](https://github.com/parttimenerd/basic-profiler-tests). This runs profiles the [Renaissance](https://renaissance.dev/) benchmark with
>> - ... different heap sizes
>> - ... different GCs
>> - ... different samplers (the standard JFR and the new CPU Time Sampler and both)
>> - ... different JFR recording durations
>> - ... different chunk-sizes
>
> Johannes Bechberger has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 127 commits:
> 
>  - Merge branch 'master' into parttimenerd_cooperative_cpu_time_sampler
>  - Add error message on signal handler install failure
>  - Fix signal handler synchronization
>  - Improve
>  - Rename autoadapt
>  - Make process_cpu_time_request private and move up
>  - Reorder condition
>  - Tiny refactoring
>  - Restrict threads for which timers are created
>  - Fix tiny mistake
>  - ... and 117 more: https://git.openjdk.org/jdk/compare/7838321b...4fd4b673

src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 647:

> 645:   // install sig handler for sig
> 646:   if ((s8)PosixSignals::install_generic_signal_handler(SIG, (void*)::handle_timer_signal) == -1) {
> 647:     log_error(jfr)("Failed to install signal handler for CPU thread sampling, possibly because another profiler is active: %s", os::strerror(os::get_last_error()));

That we are using a signal handler to provide the user with CPU time information is an implementation detail. Its good to provide an error message, but I think it should reflect back on something the user is expecting.

Perhaps add a line that says something along the lines of "CPUTimeSample events will not be recorded."

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PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2126357345